1. Field of the Invention
The present invention generally relates to mobile terminals capable of measuring biological signals, and specifically relates to such a mobile terminal having an electrode for human body earth or system reference, placed on an outer surface of a terminal body.
2. Description of the Related Art
For example, when a handicapped person such as a person having no laryngopharynx or the oral part of pharynx after undergoing a laryngectomy tries to speak in vain, what the person is trying to speak can be determined by detecting perioral muscle activities. Then a speech synthesizer is driven to produce synthetic speech in place of the person's voice.
One good example of such research works is published in Noboru Sugie et. al., A Speech Prosthesis Employing a Speech Synthesizer—Vowel Discrimination from Perioral Muscle Activities and Vowel Production, IEEE transactions on Biomedical Engineering, Vol. 32, No. 7, pp 485-490, the entire contents of which are hereby incorporated by reference.
According to the research work, the movements of the mouth are picked up via three channels of electromyography with Ag—AgCl surface electrodes. After band-pass filtering of the electromyography, a thresholding operation is performed to reduce the noise component. Then the number of crossings of the threshold level is counted for each channel. Depending on the number of the count at each time interval, each muscle is assigned a 1 or 0 to designate an active or inactive state, respectively. Then a sequence of 3-bit numbers is fed to a finite automaton for vowel discrimination out of all the five basic Japanese vowels: /a/, /e/, /i/, /o/, and /u/. The output of the automaton is used to drive a speech synthesizer for vowel production.
One example of detecting electromyography signals to discriminate between Japanese vowels is shown in Japanese Patent Laid-open publication No. 7-181888, the entire contents of which are hereby incorporated by reference.
In this example, as shown in FIG. 5, a speech synthesizer 50 includes an electromyography (EMG) signal detecting unit 15 for detecting EMG signals caused by muscle movements due to speech activities, a syllable identifying unit 11 for generating identifying signals corresponding to desired syllables, a learning unit 13 for learning based on detected signals fed from the EMG signal detecting unit 15 and the identifying signals fed from the syllable identifying unit 11, a discrimination unit 17 for receiving input patterns fed from the EMG signal detecting unit 15 and discriminating and outputting sound syllable signals corresponding to the input patterns, a sound synthesizing unit 18 for synthesizing sound signals corresponding to the sound syllable signals fed from the discrimination unit 17 and converting the sound signals to sounds, a sound outputting unit 19 for outputting the sounds converted by the sound synthesizing unit 18.
The EMG signal detecting unit 15 has a plurality of skin surface electrodes 14 for detecting EMG signals corresponding to muscle movements, amplifiers 16 for amplifying the EMG signals detected by the skin surface electrodes 14, filters (not shown) for filtering out low and high frequency components from the amplified signals, and converters (not shown) for converting the filtered signals to power spectrums. Further, after the conversion to the frequency spectrums, the components separated by band can be processed in parallel, and therefore consonant discrimination becomes possible.
In addition to such medical use, there has recently been an increasing demand for human interfacing purposes to easily obtain and process human biological signals such as electromyography signals and electroencephalogram (brain wave) signals.
When obtaining biological signals such as EMG signals or electroencephalogram signals, operational amplifiers are normally used for reducing the external noise component. A plurality of electrodes are required to be attached to a human body in order to obtain EMG signals using the operational amplifiers. For example, in order to obtain one kind of EMG signal, at least three electrodes should be attached to a human body. That is, two electrodes for the operational amplifier and one electrode for body earth or system reference are needed. Some measurement devices require one electrode dedicated to the body earth and another electrode dedicated to the system reference. In this case, four electrodes are necessary for getting one kind of EMG signal.
Out of these electrodes, two electrodes for the operational amplifiers should be attached or patched on human skin in the gliding direction of muscle and at a place to be measured. On the other hand, the place where the electrode for the body earth or the system reference is attached is not specially limited, because the electrode is attached for the purpose of getting a reference potential for the operational amplifier or equalizing the operational amplifier ground potential with the human body.
In order to attach such electrodes, an operator should apply paste to the electrodes and then attach the electrodes to human skin, and fix them on the human body using tape. These processes need a lot of time and are troublesome. With regard to the body earth electrode or the system reference electrode, a band electrode can be wrapped around an upper extremity or an arm, or a lower extremity or a leg, or a clip electrode can be used by clipping it onto a lobule of auricle or an earlobe. Even if these simple electrodes are utilized, the electrode attaching operation is still necessary and troublesome.
Conventionally, the measurement of EMG signals and electroencephalogram signals has been mainly aimed at medical clinical examination or therapy, and therefore the prior art electrodes were assumed to be used only in examination rooms or operating rooms. Therefore, where the biological signals such as EMG signal or electroencephalogram are utilized as human interfacing means, it is necessary to make the electrode attaching operation easier and simpler as much as possible to reduce user's workload. And even when the biological signals such as the EMG signals or electroencephalogram signals are used for the purposed of examination or therapy, it is much better to make the electrode attaching operation easier or simpler.
As mentioned above, in order to obtain biological signals such as EMG signals or electroencephalogram signals, it is necessary to attach two kinds of electrodes: differential electrodes, and a body earth or system reference electrode. The place where the differential electrodes should be attached is limited to areas to be measured. The place where the body earth or system reference electrode should be attached is not specially limited. Therefore, the differential electrodes have limited places to be attached, and therefore should be attached to the most appropriate portion using the best attaching method. The differential electrode is therefore usually not necessarily attached in a simple manner.
On the other hand, the body earth or the system reference electrode without limitation to the attaching places can be attached anywhere in a predetermined certain area. Therefore, if there would exist one way to attach the body earth or the system reference electrode to a certain area of a human body in a simple manner, then it would be possible to avoid trouble when attaching the electrode. Specific examples for simply attaching are the above mentioned band electrode or clip electrode.
When the biological signals such as EMG signals or electroencephalogram signals are measured for the purpose of human interface use, the utility value of the biological signal measurement would be significantly increased if such measurement could be performed without any limitation in its measuring place, and the measured results could be identified and transmitted to a remote area through wired or wireless communication.
In order to realize the above mentioned improvement, it is desired to utilize a mobile terminal such as a mobile phone or a personal digital assistant (PDA) for obtaining biological signals such as EMG signals or electroencephalogram signals. When using a mobile terminal such as a mobile phone or a PDA to measure biological signals such as EMG signals or electroencephalogram signals, it is especially important to be able to simply and easily attach an electrode for body earth or system reference to a human body.